Weir Head-Discharge Relationships: A Multi-Lab Exercise

Though weir flow has been studied for centuries, there still remains some nuances of weir flow that are not well understood. Therefore, an international study was conducted in which 20 different hydraulics laboratories from around the world built and tested two linear weirs (quarter-round and half-round crested weirs) of common geometry. The only unconstrained dimension was the weir length, which could be adjusted to match the width of the test flume. Participating laboratories used the instrumentation and data collection methodologies of their choosing for head and discharge measurements.

The experimental results found significant variability in the discharge coefficients as a function of dimensionless upstream head, as well as in the head-discharge relationships (as much as 50% in some cases). Potential sources contributing to the scatter may have included head meter instrumentation, flow meter instrumentation, approach flow length (flume length upstream of weir), head measurement location, nappe behavior, laboratory measurement methods and experimental setup, and the care and skill of the investigator (human error). Analyzing the data as a function of instrumentation types, approach length, and head measurement location did not provide any insight regarding the variations. Nappe behavior (e.g., aeration), which could be influenced by laboratory-specific conditions, varied among the datasets primarily for the half-round crested weir (about 20%).